Adiabatic Demagnetization Refrigerator for the Characterization of High-Performance Superconducting Quantum Circuits

在这份赠款申请中，我请求为绝热消磁冰箱(ADR)提供资金，这是一种低温恒温器，可以将小型机械物体和电子设备冷却到比热力学绝对零度高千分之几的温度(=摄氏零下273.15度)。这种低温恒温器的独特之处在于，它不需要任何低温液体或稀有而昂贵的氦-3气体就能达到如此低的温度。一种特殊的脉冲管将低温恒温器预冷到大约-270摄氏度。系统通过绝热退磁循环进一步冷却。这一过程类似于橡皮筋冷却：首先缓慢地(即等温地)拉伸橡皮筋，这样产生的热量就会散失。然后，你迅速(也就是绝热地)把它拉出来，然后立即测量它的温度。你会发现橡皮筋比实验开始时冷。使用顺磁性盐而不是橡皮筋，并使用磁场来“拉伸/去拉伸”盐，使温度接近绝对零度。温度与能量成正比：系统的温度越高，其热能就越大。量子力学系统的特征是一组离散的状态，每个状态都有自己的能量。为了揭示一个给定系统的量子力学性质，它的热能必须显著低于系统最低能级之间的能量分离。在这个项目中，我们将使用ADR将纳米制造的超导电路冷却到显示其量子力学行为所需的阈值温度以下。ADR是表征这种量子电路的一种快速而有效的工具，它将使我们能够选择最好的超导材料来优化器件的性能。在实现固态量子计算机的长期探索中，这是一项关键任务。我相信，ADR将使超导量子电路的质量在明年内提高十倍。物理学界和加拿大作为一个国家都将受益于在高性能固态设备的纳米制造方面获得技术专长。

In this grant application I request funding for an adiabatic demagnetization refrigerator (ADR), a type of cryostat that makes it possible to cool small mechanical objects and electronic devices to a temperature of a few thousandths of a degree above the absolute thermodynamic zero (= -273.15 degrees on the Celsius scale). This cryostat has the unique feature in that it does not require any cryogenic liquids, or the rare and expensive helium-3 gas, to reach such low temperatures. A special pulse tube pre-cools the cryostat to approximately -270 degrees Celsius. The system is further cooled by means of an adiabatic demagnetization cycle. This process is similar to a rubber band cooling: You start by stretching a rubber band slowly (i.e., isothermally) so that the generated heat is dissipated. You then rapidly (i.e., adiabatically) de-stretch it and you immediately measure its temperature. You will find that the rubber band is colder than at the beginning of the experiment. The use of a paramagnetic salt instead of a rubber band and of a magnetic field to "stretch/de-stretch" the salt allows temperatures to reach close to absolute zero. Temperature is proportional to energy: The higher the temperature of a system, the larger its thermal energy. A quantum-mechanical system is characterized by a discrete set of states, each with its own energy. In order to unveil the quantum-mechanical properties of a given system, its thermal energy must be significantly lower than the energy separation between the system lowest states. In this project, we will use an ADR to cool nano-fabricated superconducting circuits below the threshold temperature required to show their quantum-mechanical behavior. The ADR is a fast and efficient tool to characterize such quantum circuits, and it will allow us to choose the best superconducting materials to optimize the devices' performance. This is a critical task in the longstanding quest towards the implementation of a solid-state quantum computer. I believe the ADR will make it possible to improve the quality of superconducting quantum circuits by a factor ten within the next year. Both the physics community and Canada as a nation will benefit from gaining a technological expertise in the nano-fabrication of high-performance solid-state devices.